Monday, May 25, 2009

Based on studies by Rebecca A. Gooding, Christopher D. G. Harley, and Emily Tang at the University of British Columbia in Vancouver in a study to be published in PNAS next week.... (Rebecca A. Gooding, Christopher D. G. Harley, and Emily Tang. Elevated water temperature and carbon dioxide concentration increase the growth of a keystone echinoderm. PNAS Early Edition May 25, 2009) To quote directly from their interview on Mongabay:

Climate change is expected to cause widespread disruptions to ecosystems and their resident species. Some creatures will go extinct, others will expand their ranges and thrive.

A new study identifies starfish as one of the possible winners from rising ocean temperatures and carbon dioxide concentrations.

Rearing Pisaster ochraceus , a species of sea star, under varying conditions, Rebecca Gooding, Christopher Harley, and Emily Tang of the University of British Columbia in Vancouver found that increased temperature and acidity will significantly boost the echinoderm's growth rate, more than offsetting the negative effects of reduced availability of calcium carbonate, an important structural building block for many marine invertebrates. The results contrast with other research which has shown a negative correlation between increased ocean acidity and growth rates of calcifying species.

"Our findings demonstrate that increased [CO2] will not have direct negative effects on all marine invertebrates, suggesting that predictions of biotic responses to climate change should consider how different types of organisms will respond to changing climatic variables," the authors write. "Some ecologically important species... may directly benefit from acidification."

Sunday, May 17, 2009

Because CraigM asked so nice, here is a special Echinoblog in honor of SEX WEEK at Deep-Sea News. (Info for this blog from Tominaga et al., 2004, Biol. Bull 206: 25)

I thought it would be fun to write about the oh-so rare occurrence of sexually dimorphic brittle stars? What does that mean?

Males and females look different!

A pretty fundamental difference among humans (and many vertebrates)-but among most animals-only THEY seem to really know for certain!

(The Echinoblog Art Department strikes again!)

In this case..our feature critter is a species of ophiuroid or brittle star, Ophiodaphne formata, which is found in the tropical Pacific. The population studied was from Tsuruga Bay in the Sea of Japan.

First, the essentials:
1. Males are MUCH smaller then females. (see picture)
2. Males live ON females. Mouth to mouth and bursae to bursae (see picture)
3. The female of the pair adheres to the oral surface of a host sand dollar! (Astriclypeus manni)
4. Spawning occurs WHILE they are paired ON this sand dollar!

Tominaga and his co-authors observed this behavior, including spawning and full
development of the babies up to metamorphosis (i.e., they settle into very tiny adult-like animals) including the very peculiar habitat of the male+female coupling which is believed to facilitate the reproductive success of the species.

They further observe that pairing in O. formata is observed throughout the year, including the “non-breeding” season. The position of “oral to oral” coincides with the respective locations of the “bursa” on the oral surfaces that open into the gonads of each individual.

Thus, they say it is most “efficient” for the males to have their arms holding tight to the larger female, mouth to mouth while he sheds sperm from his bursal slits. (sexy!) The need to pair off together is important because of the low densities of this species relative to other, more common shallow-water species. They speculate that the “fertilization efficiency” would be low if males and females spawned separately and could not shack up on their host. Thus, the sand dollar provides the breeding site (aka the love shack!) and raises the level of “fertilization success”!!!

Sand dollars (Echinoidea) are in the superorder Gnathostomata. I always thought Gnathostomes was the grouping that was associated with the development of jaws in Chordata (as in sharks). I must be missing something. Any thoughts?

Good Question! Yes, they ARE the same. But the nomenclatural codes only mandate the use of a unique name at the family level and below. Here is the ICZN reg (from ICZN.org):

23.3. Application to Synonymy. The Principle of Priority requires that a taxon formed by bringing together into a single taxon at one rank two or more previously established nominal taxa within the family group, genus group or species group takes as its valid name the name determined in accordance with the Principle of Priority [Art. 23.1] and its Purpose [Art. 23.2], with change of suffix if required in the case of a family-group name [Art. 34].but two superfamilies, orders or higher? Permissible but not advisable for any number of reasons. In this case, the term applies to very disparate taxa (Echinodermata vs. Chordata) and the context is clear in each case-which probably explains why no one has ever sought to change one or the other.

Is there a disadvantage to sand dollars being overweighted, resulting in them being anchored to the bottom?

I don't have any data on this but based on what I've read-Yes. The inability of the sand dollar to better position itself for feeding, protection or any number of other reasons would be a huge adaptive consideration. Presumably, that's how the thinner body and lunule development came about to counter the problems with being blown away or being anchored to the bottom.

From "YouUsed2BeCool"

I was curious as to how quickly the basket stars grow?The determination of age in basket stars has been looked at in a few species. One paper (Stewart & Mladenov 1997) concluded that growth was not constant. They found the New Zealand Astrobrachion reaching an "adult" size (23.00 mm disk) in approximately 8 years. But there is the caveat that 'aging' plates in these animals is very difficult and is not thought to be really possible for some species. Also, what material comprises their tentacles?Are these basket stars able to control every since one of their tentacles?

The arms/tentacles are constructed like the arms of any other brittle star except that there is an extensive fleshy overlay covering the skeletal structure you would see in other more "ophiuran" looking brittle stars. Basket stars have additional muscles and other nerve tissue that innervate the armtips along with the hooks that are present. This paper (Rosenberg et al. 2005) has some good details on Gorgonocephalus biology.

What preys on them? (they're quite large!)Its not clear to me what will feed on one of these since there's really not much to eat, but generally speaking, big filter feeding echinoderms usually worry about fishes and/or critters that snap at their arms (such as large crabs).

How exactly do crinoids go about moving themselves from one perch to another? Do they release their foot or some sort, and just float away?

I assume you refer to comatulid (i.e., stalkless) crinoids? These move using their arms. Some comatulids are known to "creep" along the bottom using sort of a "Pull-and Push" type motion carried out by the cirri with the aid of the arms. It is thought that where there are arms of differential length, longer arms are anterior during locomotion (ref. to Lawrence 1987).And of course, they can swim...

From "Ariel Tang"

One of those videos shows that sea cucumbers spit their digestive system out when threatened. Can their digestive systems be regenerated later on? How long does it take to regenerate usually? During this period, which part help them digest? Thank you!

Sea cucumbers CAN eject their guts, which by the way includes not only the intestine-but also gonads, hemal system and etc. at an oncoming predator or other meacing entity. Some holothurians actually have specialized sticky, toxic structures called Cuvierian tubules which are used instead. In any case, if we are talking about "evisceration" and guts are used, YES they DO grow back!!

Regeneration time varies but the papers I found indicated thatmany of these species could have a completely regenerated intestinal system in 2 to 5 weeks!! (depending on species). The regenerated intestinal system is essentially identical to those of the noneviscerated animals.Presumably, during this time the animal subsists on internal reserves or absorbs nutrition via some other source (e.g., absorbtion through the body wall)-but I'm not sure.

From "Poopie Pants"

Do you know why Culcita novaeguineae have such a prominent "cushion" morphology? It seems like it would hinder locomotion and feeding.

The "cushion" morphology is actually present not only in Culcita but also most members of the family Oreasteridae. Although its not clear what developmental mechanism is responsible-its thought that the swollen body and heavy body calcificiation are defensive adaptations to living in the tropical Indo-Pacific where oreasterids are diverse and abundant.

From "mattmungo"

One would expect that if the brittle star is to exit the jelly that it would either destroy the bell part to get out or go through the oral opening and risk touching the tentacles of the jelly fish. have any studies been done to see if the brittle starts that hop on for the ride are able to touch the tentacles and not be stung? what are some possible ways for the brittle star to effectively get in and out of the jellyfish, and how does the brittle star know when it is time to jump ship?

There isn't much known about the relationship between jellies and the tiny commensal brittle stars which live inside them but brittle stars would not necessarily destroy the jelly on its way out. Jellies appear delicate and ethereal, but in fact if you've ever held the tissue from one, the texture is like really, tough, thick gelatin.

The brittle stars in question are practically weightless and both animals are largely suspended by the buoyancy of water. Some of the studies suggest that as the brittle stars get larger they may crawl or simply fall out of the bell (ophiuroids in jellies tend to be smaller)and may possibly just avoid the stings of the tentacles all together.Departing the bell may be triggered by detection of poor water quality (as was the case in one study) or simply the need for food (as other individuals of the same species are found on soft bottoms).

Why are sand dollars and star fish generally in the shape of perfect pentagons with 72 degree angles between each ray? I understand that in chemistry intermolecular forces cause molecules to take shapes such as this, but since this is much large scale than that of a single compound molecule, what force dictates this perfect symmetry shape? for example why aren't some of the rays 35 degrees apart and so on and so fourth?

hmmm..thats' a good one. I've heard discussions about the physical-chemical constraints of calcium carbonate effect on the overall body form of echinoderm but honestly, I'm not sure that what you're seeing is a reflection of this.

Bear in mind that the bodies of echinoderms are millions of tiny pieces that are held together/embedded in tissue. There may be some overall physical constraints that make it easier for some groups of animals to form pentagons then others-but there is a huge diversity in echinoderm body forms. Especially when you look at the fossil record. See my blog about the Paleozoic Helicoplacoidea (click) as an example of an early echinoderm body form that does NOT show pentagonal body symmetry. But at one level, you're right many echinoderms display this natural symmetry but I'm not sure what the answer is...

From "Joshua Hallas"

I was wondering if there are any other examples of echinoderms living in symbiosis with other cnidarians? and are the brittle stars parasitic or commensal?

Lots of brittle stars live as commensals on corals and their kin...you can go to this post for some idea of the relationship! In many of these relationships, the brittle stars aren't thought to prey on their "hosts" which act primarily as perches for better suspension feeding or homes for the animals to live in. None of these echinoderms are really known to be truly parasitic in the sense that say, nematodes or other invertebrates are.

From "AnthonyM"Is there a chance that instead of thinking they are using the jelly fish as transport or protection that maybe they just happened to be there by accident? And if not how do the jelly fish react to all these different inhabitants?

uh...well, its not an "accident" as you put it. As it sez in the blog, the densities in some specimens some get quite high. Over 800 in that one instance. Its not frequently encountered..but there are many consistent reports.

Its not really known how they affect the jelly much but like many such commensals they are just along for the ride...think of it as much the same way ticks and mites ride in your eyebrows or barnacles ride on whales..

From "Rene"I understand that the ossicles of echinoderms are connected by ligaments composed mainly of collagen; in addition, these ligaments are mutable at short timescales, under neural control. Is it safe to call this structure a form of muscle?

This is an interesting notion and is currently a topic under some discussion in the scientific community. I would go to this paper by Takemae & Motokawa (2005) Ultimately, though Mutable Collagenous Tissue is composed of ligaments and not muscle cells. So, MCT does behave like muscle, but for various other reasons is NOT itself muscle. There's more to this then I can cover here..so I would recommend going to the ref and trying to track down the back-and-forth between the different 'camps' discussing the issue.

On one of my trips to the S.F. Academy of science I came across the water tank of a Fire Urchin. The animal was on its oral side suctioned to the glass via its tube feet. I decided to take a picture of the animal with my phone. When I reviewed my picture I noticed that there were five bright purple dots. When I glance back at the animal I could not see them. The bright purple dots seem to become visible only on the photo. Do urchins in general have some sort of bioluminescence?

So, I suspect you have seen something like what you would see in this picture or this one... This is probably iridescence-the reflection of light from your picture and not bioluminescence, which is the generation of light by the animal and/or its symbionts. There are bioluminescent sea-urchins which live in the deep-sea, but "fire urchins" which is a common name for one of several tropical species often just have these bright reflective blue interradial regions. I'm not sure what they do aside from contrast to the fiery red...but they are a something you would be more inclined to see with light bouncing off them...

Thanks to the Biol 555 and Dr. Rebecca Johnson for participating!!!

Those were some GREAT questions!!!

Do you have an enthusiastic Invertebrate Zoology Class which would like to ASK THE ECHINOBLOG??? Contact me via my profile....

Simply put, the warming of the waters makes the Southern Ocean more vulnerable to invasive species as well as faunas from the surrounding area. The unique fauna of Antarctica, of which I have featured hereand hereare in danger of being exposed to new predators and environmental changes.

The authors urge treaty nations to take steps towards protecting the pristine and unique environment/ecosystem that is found in Antarctica and elaborate on concerns from increasingly more frequent outside environmental threats, such as tourism and the potential for increased biological invasions.Changes in Political Attitudes Toward Antarctica???The authors touch on this subject. We have already seen claims by several countries as we have observed the change in Arctic glacial cover.

There are apparently also claims by countries via the UN Convention on the Law of the Sea (UNCLOS) which includes part of the seafloor beneath the Southern Ocean. This brings us to this:

As the world's fossil-fuel crisis deepens and developing economies increase their demand for limited natural resources, Antarctica will become a focus of intensive resource exploitation. It is crucial for the international community to anticipate these developments in order to have policy in place, and we (Thatje & Aronson) propose that the UN take up this issue immediately. Polar ecosystems are among the least disturbed but most vulnerable ecosystems on the planet (Halpern et al., 2008, Science 319: 948). In the end, we are left with the fundamental ethical question: are we willing to risk the last pristine places on Earth??? (emphasis is mine)

Tuesday, May 5, 2009

This 2007 research expedition for new species aboard the RV Presbitero began in the port of Manila and then south through the Sulu Sea to our study site, southeast of the Sulu Archipelago. The bottom falls off abruptly to the sea floor 5000 thousand meters below. Lying just north of the equator, the Celebes Sea is the center of the most biologically diverse area of the world's ocean.

Rhopilema sp.Based on the locality of Mozambique, this is probably O. marmorata on Rhopilema nomadica.This also is a good time for me to mention why the increasing availability of nature photography is such an incredible asset to biologists everywhere. I'm pretty sure that the image has captured a novel occurrence maybe even a new one for this region...

If one looks closely..one sees that its not just one or two but MANY brittle stars along for the ride!!

Prior records of this species from Mozambiuqe record a jellyfish with ca. 250 mm diameter with 20 to 50 ophiuroids found on the bell!!! (along with a bunch of pontoniine shrimps! clinging to the oral arms). One record from India recorded 829 ophiuroids one one jellyfish with a 280 mm diameter bell!!

Oral arms are the long extensions which hang off the bell around the mouth...Curiously, a panoply of miscelleous critters live in and around the oral arms.. presumably to take advantage of the jellyfish feeding...But...WHY??
and ya' know...that's a good question. So far two explanations have been offered...

1. Food & Protection?Ophiocnemis and other ophiotrichids are small particle feeders and have a great many spines all over their body. They live in and around the oral arms. Perhaps the pelagic larvae, known as an ophiopluteus, which looks like this:

Is attracted or settles in and around the mouth or the animal in general? Could they be attracted to currents? Or some other physical feature?? Protection until they get larger?

2. Dispersal via 'rafting' Adding a further layer to all of this? Not all of these live in jellyfish. In fact, its been suggested that only smaller ones live on jellyfish, suggesting that they eventually have to 'fall off' the ride..
But Ophiocnemis certainly gets around! Australia, India, Mozambique-all over the tropics! and on a great variety of jellyfish hosts!

This is one of those weird and wonderful things about echinoderms! Sometimes just knowing that it does this weird frakking thing is just the beginning!!!

About Me

I pursue starfish related adventure around the world with a critical eye and an appreciation for weirdness.
Support has been courtesy of the National Science Foundation but the views and opinions presented herein are mine and do not reflect the opinions of them or any affiliated institutions.
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